Arrangement for multi-stage heat pump assembly

ABSTRACT

A gasdynamic arrangement for a multi-stage centrifugal turbomachine, such as a two-stage compressor, comprising two coaxial impellers assembled on a common shaft with axial intake ports and radial peripheral discharge zones, the intake ports of the two impellers preferably pointing away from each other; a cylindrical vessel concentrically housing the impellers and the intake duct; a partition wall between the two impellers having a first and a second group of apertures; a first array of curved ducts conveying the flow from the first impeller discharge zone to the first group of apertures in the partition wall, the flow further passing through a chamber in the vessel to the intake port of the second impeller, and a second array of curved ducts conveying the flow from the second impeller discharge zone to the second group of apertures in the partition wall, the flow further going to the discharge port, the two flows bypassing each other in opposing directions at the partition wall.

FIELD OF THE INVENTION

[0001] This invention relates generally to gasdynamic schemes inturbomachines such as centrifugal compressors used in heat pumps, andmore particularly to compact gasdynamic arrangements for high-capacitymultistage centrifugal compressors working with water vapor.

STATUS OF PRIOR ART

[0002] Various industrial applications, e.g. desalination, waterchilling, and ice-making, require massive production of cold, i.e.cooling large quantities of air, water or other coolant. A known methodof absorbing heat, when water is used as coolant, is boiling the coolantwater under reduced pressure at the respective low temperature. In orderto dispose of the heat contained in the evaporated water, the vapor mustbe brought to higher temperature and pressure by suitable thermodynamicprocess and finally be condensed transferring the heat to an availableheat sink such as water from a cooling tower. The temperature differencebetween the compressed vapor and the heat sink, plus some additionaltemperature drop needed to drive the dynamic heat transfer, allexpressed in units of the saturated water vapor at those temperatures,determine the compression ratio (CR) of the compressor powering thisprocess.

[0003] From the viewpoint of economics, it is desirable to employ thecompression process in a single-stage compressor. But when by reason ofvarious design considerations, a single-stage compressor is impractical,it is then the practice to use two or more compressor stages in series,as disclosed in the U.S. Pat. No. 5,520,008 to Ophir et al. Implementingintercooling of the gas/vapor between stages raises the thermodynamicefficiency of the operation and lowers the consumption of mechanicalpower.

[0004] In the heat pump assembly described in the Ophir et al. patent,use is made of a pair of individual centrifugal compressor units, eachhaving its own impeller shaft and a bearing house therefor, as well asits own motor to drive the shaft. In this arrangement, the two motorsare placed on opposite sides of the compressor chamber.

[0005] In a multi-stage centrifugal compressor in which the stages areassembled in series, the geometries of the vapor passages must becarefully designed so as to convey in an energy-efficient manner thepartially compressed vapors from the discharge zone of a preceding stageat the periphery of its impeller to the central intake port of thesucceeding stage. Often, intercooling of vapors between the stages isrequired in order to attain optimum thermodynamic efficiences. Theserequirements further complicate the geometry of the vapor passages, andalso enlarge the physical dimensions and cost of the heat pump assembly.This is especially true of high throughput heat pump units of largediameters.

[0006] Such machines as in U.S. Pat. No. 5,520,008 have been built andare operating well, but a more compact solution is very desirable, inorder to reduce cost and facilitate installation and maintenance work inconfined spaces, such as service basements and galleries of largehotels, office buildings, shopping centers, etc.

[0007] A more compact arrangement is disclosed in DE 1803958A describinga two-stage turbomachine (compressor) with intermediate heat exchangerswhere the impellers of the two stages are disposed coaxially opposite toeach other and constitute one body. The intake duct of the turbomachineis a cylinder or conical pipe coaxial with the impellers and is disposedat the side of the first stage. The discharge flow of the first stage isconveyed by a plurality of first discharge ducts to an annular heatexchanger coaxial with the impellers, embracing the intake duct anddisposed also at the side of the first stage. Then the flow makes asharp turn by 180° into a peripheral annular channel embracing the heatexchanger and is directed to the intake port of the second stage. Thedischarge flow of the second stage is conveyed by a plurality of seconddischarge ducts to another annular coaxial heat exchanger ending with adischarge port and disposed between the intake duct and the first heatexchanger, also at the side of the first stage. This arrangement placesfour coaxial flows and two heat exchanger volumes at one side of theimpeller group, which involves high hydraulic losses.

[0008] CH 102821 discloses a four-stage turbomachine (compressor) withtwo parallel shafts driven by one motor by means of a gearbox. The firstand the second stage impellers are on one shaft, in opposition, whilethe third and the fourth stage impellers are on a second shaft. Theintake duct is disposed laterally to the first shaft. The discharge ductof the first stage conveys the flow from the periphery of the firstimpeller to the intake of the second stage along a path approximatelyfollowing the surface of a torus coaxial with the first shaft, while thedischarge flow of the second stage is gathered in a space defined by thesame torus and conveyed via one lateral pipe to the intake of the thirdstage coaxial with the second shaft. This arrangement is asymmetric anddoes not accommodate heat exchangers or other elements in the flow pathbetween coaxial stages.

SUMMARY OF THE INVENTION

[0009] In view of the foregoing, the main object of the invention is toprovide novel gasdynamic arrangements particularly suitable for buildingeconomically feasible, compact and efficient turbomachines such asmulti-stage, high-compression, high-throughput gas or vapor centrifugalcompressors for heat pumps, and a novel design of a heat pumpparticularly suitable for use with such compressors.

[0010] In accordance with a first aspect of the present invention thereis provided a gasdynamic arrangement for a multi-stage centrifugalturbomachine having an intake duct and a discharge port, comprising:

[0011] two impellers with axial intake ports and radial peripheraldischarge zones, the intake port of the first impeller being in fluidcommunication with the intake duct, the two impellers being located attwo sides of an imaginary plane crossing their common axis;

[0012] a first means for conducting the flow from the peripheraldischarge zone of the first impeller to the intake port of the secondimpeller along a first flow path including a plurality of first curvedducts in axysimmetric arrangement;

[0013] a second means for conducting the flow from the peripheraldischarge zone of the second impeller towards the discharge port of themachine along a second flow path including a plurality of second curvedcuts in axysimmetric arrangement;

[0014] wherein the first and the second paths leave the respectiveperipheral discharge zones bending gradually towards the imaginaryplane, cross the imaginary plane in opposite directions and, after thecrossing, the two flow paths lie entirely at different sides of theimaginary plane.

[0015] In a particular embodiment of a two-stage compressor thegasdynamic arrangement comprises:

[0016] two coaxial impellers assembled on a common shaft, the intakeports of the impellers preferably pointing away from each other;

[0017] a cylindrical vessel concentrically housing the impellers and theintake duct;

[0018] a partition wall between the two impellers having a first and asecond group of apertures;

[0019] a first array of curved ducts conveying the flow from the firstimpeller discharge zone to the first group of apertures in the partitionwall, the flow further passing through a chamber in the vessel to theintake port of the second impeller, and a second array of curved ductsconveying the flow from the second impeller discharge zone to the secondgroup of apertures in the partition wall, the flow further going to thedischarge port, the two flows bypassing each other in opposingdirections at the partition wall.

[0020] In accordance with a second aspect of the present invention,there is provided a gasdynamic arrangement comprising an annularcondenser chamber disposed concentrically around an intake duct within aheat pump assembly.

[0021] Both aspects are aimed at the development of more compactturbomachine designs. In the implementation of the arrangement of thefirst aspect of the present invention in a two-stage compressor, this isachieved by the usage of a short common shaft supported by a singlebearing house situated between the impellers (stages) and driven by asingle motor. In the implementation of the arrangement of the secondaspect of the present invention in a heat pump assembly, this isachieved by a reduction of the assembly overall length. The employmentof both gasdynamic arrangements provides for a highly integrated heatpump assembly, wherein all functional components of the system with thepossible exception of the driving motor—multiple compressor stages,evaporator, condenser, intercooling and mist-elimination equipment—areincorporated within a single cylindrical vessel without external ducts.The assembly is characterized by reduced gas/vapor pressure losses,thereby improving the compression ratio and enhancing heat pump economy.The cost of manufacturing this integrated heat pump assembly isconsiderably lower than the cost of manufacturing an assembly having thesame capacity composed of separate units with interconnecting externalducts. The structured configuration of the integrated assembly greatlysimplifies its erection at an operating site.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] For a better understanding of the invention as well as otherobjects and features thereof, reference is made to the attached drawingswherein:

[0023]FIG. 1 schematically illustrates one embodiment of a two-stageheat pump assembly in accordance with the invention.

[0024]FIG. 2 is a perspective view of the crown arrangement of opposingdiffuser ducts and impellers in the two-stage compressor, and

[0025]FIG. 3 schematically illustrates a second embodiment of the heatpump assembly having three stages.

DESCRIPTION OF THE INVENTION

[0026] In accordance with a first embodiment of the present invention, aheat pump and a two-sage compressor are shown in FIG. 1. The heat pumpis an integrated heat pump assembly based on an gasdynamic arrangementin accordance with the invention, all components of the assembly, exceptfor the motor 10, being contained within a cylindrical vessel 11.

[0027] The vessel is divided by partition walls 12 and 13 into anevaporator chamber A, a condenser chamber B and a compressor chamber C.The evaporator chamber A is equipped with headers 15 adapted to spreadentrant water or other coolant in thin “curtains” with a large surfacearea to promote its evaporation under partial vacuum conditions.

[0028] Evaporator chamber A opens into an intake duct 16 leading intothe intake port of the compressor. The inlet of intake duct 16 iscovered by a mist eliminator 19 preventing the entrance of waterdroplets. Intake duct 16 is coaxial with the cylindrical vessel 11, and,together with partitions 12 and 13, defines the annular condenserchamber B. In the condenser chamber B, there is a plurality of nozzles22 mounted on the cylindrical wall of the vessel 11 and adapted to spraycooling water into the chamber.

[0029] Compressor chamber C houses the first and second stages of acentrifugal compressor, both coaxial with vessel 11. Chamber C issubdivided into two cells C1 and C2 by an intermediate partition wall 24placed between the two compressor stages. The first stage is providedwith an impeller 26 rotatable within a stationary shroud 27 and isadapted to discharge partially compressed vapor through an array ofdiffuser ducts 28 through partition wall 24 and cell C2 toward theintake port of the second compressor stage impeller 29. The annular cellC2 is equipped with means for intercooling or de-superheating the vaporbetween the two compressor stages such as water spray nozzles 31. In theflow path to the intake port of the second stage, there is provided amist eliminator 33.

[0030] The second stage impeller 29 is rotatable within a stationaryshroud 35 and is adapted to discharge compressed vapor through an arrayof diffuser ducts 37 and apertures in partition wall 24 into the annularcell C1 of the compressor chamber C which opens into condenser chamber Bthrough a discharge port 38.

[0031] Impellers 26 and 29 of the first and second stages of thecompressor are mounted on a common shaft 40 supported by a bearing house42 disposed between them. Shaft 40 is coupled to the external motor 10through a gear box 43. Thus a single motor can concurrently drive bothstages of the compressor.

[0032] As indicated by arrows, water vapor generated in evaporatorchamber A is drawn by a suction force produced by the compressor to thefirst stage intake via mist eliminator 19 and intake duct 16. The firststage impeller 26 partially compresses the vapor and discharges it tosecond stage intake via diffuser ducts 28 and cell C2, through misteliminator 33. In cell C2, partially compressed vapor is de-superheatedby cool water sprayed from nozzles 31 or by suitable heat exchangesurfaces (not shown in FIG. 1).

[0033] The second stage impeller 29 completes vapor compression andsends the vapor to cell C1 of compressor chamber C via diffuser ducts37. Next, vapor enters annular condenser chamber B and is condensedthere by means of cooling water sprayed from nozzles 22. The heatedcooling water leaves condenser chamber B through outlet 44. The chilledwater is pumped through outlet 45.

[0034] The flow path of the vapor between compressor stages is organizedin a unique gasdynamic arrangement shown in FIG. 2. The discharge ofboth impellers leaving the shroud in radial direction through theperipheral discharge zone 46 is conveyed by a plurality of curved ducts28 and 37. Ducts 28 form a crown-like array around the first impeller26, each duct bending gradually towards partition wall 24 (not shown inFIG. 2) and ending in an aperture P1 in said wall. Ducts 37 form asimilar array around the second impeller 29 and also end in apertures P2on partition wall 24 but from the opposite side. The apertures P1 and P2are arranged in an alternating pattern on partition wall 24 allowing theopposite vapor flows from the two impellers to bypass each other in avery effective way. Ducts 28 and 37 have a diffuser form, with thecross-section area gradually increasing from impeller periphery 46 topartition wall 24, whereby the vapor flow slows down and its pressureincreases.

[0035] Reverting to FIG. 1, the vapor stream indicated by arrows greatlyslows down in diffuser ducts 37, passes through discharge port 38, andflows into condenser chamber B surrounding the intake duct 16. Thisgasdynamic arrangement saves space and, together with theabove-mentioned mutual by-pass of the impeller discharge flows, allows avery compact and aerodynamically effective layout of the heat pumpassembly. The layout is also mechanically effective since the shorttwin-impeller shaft can be supported by one bearing house and driven bya short shaft line. The whole heat pump assembly with the exception ofthe motor can thus be accommodated in a simple cylindrical housing ofapproximately twice the impellers' diameter.

[0036] This configuration substantially reduces the cost ofmanufacturing and installing the assembly, simplifying to a significantdegree the erection and maintenance of the assembly at its site ofservice. It also minimizes gas/vapor pressure losses, thereby improvingthe compression ratio and the efficiency of the assembly.

[0037] The assembly as a whole can be made even more compact by placinga suitably designed electric motor between the two impellers instead ofthe bearing house, the shaft line and the external motor.

[0038] Another embodiment of a heat pump assembly of the presentinvention is shown in FIG. 3 and demonstrates the manner in which atwo-stage compressor may be expanded to three stages and more. Thearrangement is identical to that shown in FIG. 1 except that it includesa third compressor stage introduced next to intake duct 16. Impeller 48of the third stage is mounted on an extension 50 of drive shaft 40,which extension is supported by a second bearing house 52 coaxial withthe cylindrical vessel 11. Impeller 48 is rotatable in a shroud 53.

[0039] A second partition wall 54 is introduced, with apertures P1′ andP2′ similar to apertures in partition wall 24. The peripheral dischargezone of impeller 48 is connected to apertures P1′ on partition wall 54by a crown-like array of diffuser ducts 57 similar to ducts 28. Ducts37, from the peripheral discharge zone of second impeller 29 toapertures P2 on partition wall 24, are extended to apertures P2′ on thesecond partition wall 54.

[0040] A new cell C3 is defined between partition walls 24 and 54adapted to convey compressed vapor from third stage impeller 48 viadiffuser ducts 57 to the intake port of first stage impeller 26.Intercooling spray heads 61 may be accommodated in the new cell C3, inwhich case an intermediate partition wall 63 carrying mist eliminators65 is introduced in the flow path, and diffuser ducts 57 are extended tointermediate partition wall 63.

[0041] From gasdynamic point of view, impellers 48, 26, and 29 shouldnow be designated first, second, and third stage impellers,respectively. It can be readily seen from the above that more stages maybe introduced in exactly the same manner downstream of intake duct 16.

[0042] While there have been shown preferred embodiments of theinvention, it is to be understood that many changes may be made thereinwithout departing from the spirit of the invention. Thus, the assembly,instead of containing within the cylindrical vessel a multi-stagecentrifugal compressor, may contain in concentric relation with thevessel a single stage compressor.

1. Gasdynamic arrangement for a multi-stage centrifugal turbomachinehaving an intake duct (16) and a discharge port (38), and comprising: a)a first impeller (26) with axial intake port and radial peripheraldischarge zone, said axial intake port being in fluid communication withsaid intake duct; b) a second impeller (29) with axial intake port andradial peripheral discharge zone, said second impeller disposedcoaxially with said first impeller, the two impellers being located attwo sides of an imaginary plane (24) crossing their common axis; c) afirst means for conducting the flow from the peripheral discharge zoneof the first impeller to the intake port of the second impeller along afirst flow path (28, C2) including a plurality of first curved ducts(28) in axisymmetric arrangement; d) a second means for conducting theflow from the peripheral discharge zone of the second impeller towardssaid discharge port of the machine along a second flow path (37, C1)including a plurality of second curved ducts (37) in axisymmetricarrangement; characterized in that said first and said second flow paths(28, 37) leave the respective peripheral discharge zones bendinggradually towards said imaginary plane (24), said first and said secondflow paths cross said imaginary plane in opposite directions and, aftercrossing said imaginary plane, the two flow paths lie entirely atdifferent sides of the imaginary plane.
 2. Gasdynamic arrangementaccording to claim 1, comprising a partition wall (24) between saidimpellers (26, 29), said wall lying substantially in said imaginaryplane and having a plurality of first apertures (P1) and a plurality ofsecond apertures (P2), wherein: a) said plurality of first curved ducts(28) connects the peripheral discharge zone of the first impeller (26)to said plurality of first apertures P1, and said first means forconducting the flow further comprises a first outer shell (C1) defining,together with said partition wall (24), a chamber conducting the flowfrom said plurality of first apertures P1 to the intake of the secondimpeller (29), said chamber at least partially encompassing said secondimpeller; b) said plurality of second curved ducts (37) connects theperipheral discharge zone of the second impeller (29) to said pluralityof second apertures (P2), and said second means for conducting the flowfurther comprises a second outer shell (C2) defining, together with saidpartition wall (24), a chamber conducting the flow from said pluralityof second apertures (P2) towards said discharge port (38).
 3. Gasdynamicarrangement according to claim 2, wherein: a) said plurality of firstcurved ducts (28) are arranged in a first crown array around the firstimpeller (26); b) said plurality of second curved ducts (37) arearranged in a second crown array around the second impeller (29); c)said plurality of first apertures (P1) on the partition wall (24)connected to the plurality of first curved ducts (28) are positioned inalternating pattern between said plurality of second apertures (P2)connected to the plurality of second curved ducts (37).
 4. Gasdynamicarrangement according to claim 2 or 3, wherein said curved ducts have adiffuser shape with cross-section area increasing from the impellerperiphery discharge zone to said apertures in the partition wall. 5.Gasdynamic arrangement according to any one of claims 2 to 4, whereinsaid turbomachine is encased in a substantially integral axisymmetricshell (C) coaxial with said impellers (26, 29), said first and secondouter shells (C1, C2) being part of said integral shell.
 6. Gasdynamicarrangement according to claim 5, wherein said discharge port (38) ofthe turbomachine is located substantially at the same side of saidintegral shell (C) as the inlet of said intake duct (16).
 7. Gasdynamicarrangement according to claim 5 or 6, wherein said integralaxisymmetric shell (C) is formed as a cylinder with diameterapproximately twice the diameter of the impellers.
 8. Gasdynamicarrangement for a multi-stage centrifugal turbomachine according to anyone of claims 2 to 7, wherein said fluid communication between theintake port of the first impeller (26) and the intake duct (16) isperformed via at least one additional stage in the following way: a) anadditional impeller (48) having an axial intake port and a radialperipheral discharge zone is disposed coaxially between said intake ductand said intake port of the first impeller, the intake port of theadditional impeller being at the side of and connected to the intakeduct (16); b) an additional partition wall (54) with a plurality offirst apertures (P1′) and a plurality of second apertures (P2′) issituated between the additional impeller (48) and the intake port of thefirst impeller in a plane perpendicular to the axis of the impellers; c)an additional plurality of curved ducts (57) is added to connect theperipheral discharge zone of the additional impeller to said pluralityof first apertures (P1′) on the additional partition wall (54); d) saidplurality of second curved ducts (37) connecting the peripheraldischarge zone of the second impeller (29) to the plurality of secondapertures (P2) in the existing partition wall (24) is extended to theplurality of second apertures (P2′) in the additional partition wall(54).
 9. A multi-stage centrifugal compressor having the gasdynamicarrangement for multi-stage turbomachine according to any one of claims1 to
 8. 10. A two-stage centrifugal compressor according to claim 9,wherein said first and second impeller are mounted on a common impellershaft (40) adapted to be driven by one motor (10).
 11. A two-stagecentrifugal compressor according to claim 10, wherein said impellershaft (40) is supported by one bearing house (42) disposed between saidfirst and second impellers.
 12. A two-stage centrifugal compressoraccording to claim 10, wherein said common impeller shaft is the shaftof said motor, said impellers being mounted on the two ends of saidshaft.
 13. A heat pump comprising a two-stage centrifugal compressoraccording to any one of claims 9 to 12 with an intake duct (16), adischarge port (38), and a driving motor (10), the heat pump furthercomprising an evaporation chamber (A) in fluid connection with saidintake duct and a condenser chamber (B) in fluid connection with saiddischarge port, and an integral axisymmetric housing (11) accommodatingall elements of said pump or all elements except for the driving motor.14. A heat pump according to claim 13, wherein said integral housing(11) is divided into chambers by transverse separation walls (12, 13),said chambers being arranged in the following order along the axis ofthe housing: a) evaporator chamber (A), b) condenser chamber (B)surrounding said intake duct (16), c) compressor chamber (C), theevaporator chamber (A) being opened towards the intake duct (16), thedischarge port (38) of said two-stage compressor being opened towardssaid condenser chamber (B).
 15. A heat pump according to claim 14,wherein said heat pump comprises further: means (15) to feed water intosaid evaporator chamber; means (22) to spray water into said condenserchamber; means (45) to pump out chilled water; means (44) to pump outheated cooling water; and at least one of the following devices: means(33) for mist elimination situated prior to flow entry into impellerintake ports; means (31) for intercooling the compressed gas situated inthe flow path between said impellers.
 16. A heat pump according to claim13, wherein said condenser chamber (B) is arranged as an annular chamberaround said intake duct (16), said discharge port (38) opening into saidcondenser chamber.